## Magnets to stop car crashes.

Hi, new here.

So lets say a car and truck were on collision courses with these magnetic bumpers equipped, wouldn't the trucks bumper field be higher than the cars? If so i could imagine the car being repeled downward and into a flip, at which point the car would pulled towards the trucks bumper, because once the car goes into a flip it exposes its metal parts to the trucks bumper field.

Did that make any sense? If so, does it work (in theory)?

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Welcome to PF.
 Quote by MikeCB Hi, new here. So lets say a car and truck were on collision courses with these magnetic bumpers equipped, wouldn't the trucks bumper field be higher than the cars?
Not necessarily. That would depend on the strength of the magnets, which could be made the same for both cars and trucks.
 If so i could imagine the car being repeled downward and into a flip, at which point the car would pulled towards the trucks bumper, because once the car goes into a flip it exposes its metal parts to the trucks bumper field. Did that make any sense? If so, does it work (in theory)?
It is possible, in theory, that the cars lighter mass would make it prone to doing this.

 wouldn't the trucks bumper field be higher than the cars?
 Quote by Redbelly98 Not necessarily. That would depend on the strength of the magnets, which could be made the same for both cars and trucks.
He means wouldn't it be physically higher, i.e. as measured from the ground .

 i could imagine the car being repeled downward and into a flip, at which point the car would pulled towards the trucks bumper, because once the car goes into a flip it exposes its metal parts to the trucks bumper field.
You raise an excellent point that should have been obvious earlier. The two magnets interacting would only bring the car to a stop if they were properly aligned and the vehicles were constrained to narrow paths. In all other case the magnets will still repel each other, true, but in a highly unstable way, not unlike bouncing a ball on top of another ball. And the momentum will be preserved.

The most dramatic and common effect would be to put the car(s) into a spin and thus completely out-of-control.

And yes, magnets that powerful will strongly attract the metal in the car, meaning the cars will slam back together.

I was foolish to think this idea had some merit. Anyone who has played with a couple of magnets, trying to balance then and bounce them off each other will know that it is a useless feat. They will spin and collide.

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 Quote by DaveC426913 He means wouldn't it be physically higher, i.e. as measured from the ground.
Oh! Thanks for clearing that up

 This is clearly not going to work out
 The car magnet idea might not work, but I'm new to this and you all have sure made my brain work. :)
 some mechanism which can measure the speeds of incoming cars, send signals, pulls up breaks and activates some magnetic repulsion, saves the day for two cars onto each other but there are other objects which can be a problem. but the idea is cool and should be used in the time to come......
 What if we lay out a thin layering of magnets around the bottom portion of the car, said layer would have a positive charge. And the we could modify the magnets by connecting them to the cars power so that the strength of the magnetic would be directly affected by the speed and power exerted by the car. We could also attach small sensors on seperate areas of the magnetic layering so that if scrap metal does get attached to a section, then the power to that area would go to 0 and the scrap metal would fall off.

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 Quote by ElCuabnito What if we lay out a thin layering of magnets around the bottom portion of the car, said layer would have a positive charge. And the we could modify the magnets by connecting them to the cars power so that the strength of the magnetic would be directly affected by the speed and power exerted by the car. We could also attach small sensors on seperate areas of the magnetic layering so that if scrap metal does get attached to a section, then the power to that area would go to 0 and the scrap metal would fall off.
I believe page 1 explains the why the basic idea simply isn't feasible. The rest of the thread kind of hammers it in.

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 Quote by ElCuabnito What if we lay out a thin layering of magnets around the bottom portion of the car, said layer would have a positive charge. And the we could modify the magnets by connecting them to the cars power so that the strength of the magnetic would be directly affected by the speed and power exerted by the car. We could also attach small sensors on seperate areas of the magnetic layering so that if scrap metal does get attached to a section, then the power to that area would go to 0 and the scrap metal would fall off.
Oh! I didn't know we had two magnets on car bumper threads.

I missed this one.

But I like your idea of collecting scrap metal with cars. Only I'd turn the magnets off when I got home. Scrap metal is valuable.

The linked thread above contains the calculations I performed on magnetic car bumpers.

And I did solve one of the problems mentioned in both threads with a Halbach array.

Though I still don't think they will prevent car crashes, I have come up with a different use for magnets in bumpers:

Tailgaters. When people insist on tailgating, they are psychologically pushing the car in front of them. Why not let them really do it, safely, with magnets! I'd be getting about 500 mpg if we could get these installed on everyones cars.

 Obviosly the producers of Top-gear have no previous education in classical physics. I never saw the episode but, there is no magnet that would offset the potentially huge amount of POTENTIAL ENERGY stored up in the mass x acceleration of the vehicle to offset any magnetic repulsion. Now, if there was a large NEO magnet underneath the vehicle, that was suspended 1/4 inch off the ground, and the vehicle was at a constant rate of acceleration, then the car would slow down substantially if it were to transition from blacktop to a solid billet of aluminum it was moving over. In Washington state, Department of Transportation do have trucks that have massive retractable crash boxes that do crumple in the event a car were to hit it. These are there to protect the workers. BTW does anyone here have a good source of Rare Earth Neo magnets of different sizes that is very competitive in price?

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 Quote by Spikeywan No question, I just wanted to share a thought... I saw a very old episode of Top Gear last night, where he put magnets onto the front of two model cars, and drove them at each other. Because the magnets were orientated so that they would repel, the cars couldn't crash. This was given as a way of preventing accidents. However, if this was done with real cars, although the cars wouldn't touch each other, they would sustain just as much damage as if they had hit.
It would be pretty hard to drive east or west with 500kg neodymium magnets in the front

Instead, use a 1 meter thick block of EPP foam

Vidar

 My initial thought was... wouldn't giant magnets like that mess with cell phones and heart monitors anyway?

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 Quote by Low-Q It would be pretty hard to drive east or west with 500kg neodymium magnets in the front Instead, use a 1 meter thick block of EPP foam Vidar
500 kg!

By my calculations, from my $800 6" diameter x 2" thick magnet, that would cost roughly$400,000!

Calculations on how to fit all those magnets(500!) on a vehicle not attempted.

56.5 cubic inches for a 6" x 2" magnet
7.00 specific gravity of neodymium
0.0164 weight of 1 cubic inch of water in kg
6.49 kg of $800 magnet 500 kg of magnets on Vidars car 506 magnets$405,189 never mind

 Recognitions: Gold Member Science Advisor Did anyone consider the extra MASS that would be involved for a strong enough magnet? If this idea was on TV it must have been April 1st, I think.
 Permanent magnets won't do. But, how about an electromagnet that turns on when a crash is occurring? But, it would require a pulsed energy supply with an energy comparable to a car crash, over a few milliseconds. Then some dude decides to hack the energy systems into a railgun power source...

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 Quote by Khashishi Permanent magnets won't do. But, how about an electromagnet that turns on when a crash is occurring? But, it would require a pulsed energy supply with an energy comparable to a car crash, over a few milliseconds. Then some dude decides to hack the energy systems into a railgun power source...
No, the entire idea of using magnets to make an accident safer is completely bogus. Other than the fact that it isn't going to work, for the cost, weight, and complexity of such a system you could simply add passive features that would actually save lives.